1. Field of the Invention
The present invention relates to an image display apparatus such as a head mounted display which is mounted on the head to see a video image.
2. Related Background Art
Recently, image display apparatuses called head mounted displays (HMDS) which are mounted on the heads to see video images projected on display units are used for the purpose of seeing video images or screens of personal computers.
An HMD realizes appreciation of videos and the like anywhere without any influence on ambience. However, since it is mounted on the head, a demand has arisen for a lightweight apparatus with light fitting properties or a portable apparatus easy to detach. In addition, a portable facsimile image display apparatus which aims at seeing a facsimile image, or a portable image display apparatus such as a portable video phone has also been proposed.
As an HMD, an apparatus using a half mirror and concave mirror as an optical system and an LCD panel or a transmission liquid crystal display as a display element, which illuminates the LCD panel with backlight to see an image on the LCD panel is disclosed in Japanese Laid-Open Patent Application No. 8-251510. The present applicant has also proposed an optical system suitable for an HMD in Japanese Laid-Open Patent Application No. 7-104209.
As a portable image display apparatus, a transceiver having a small virtual image display is disclosed in Japanese Laid-Open Patent Application No. 7-235892. A display element and optical system suitable for this apparatus are disclosed in Japanese Laid-Open Patent Application No. 8-327920.
However, since the HMD disclosed in Japanese Laid-Open Patent Application No. 8-251510 uses a half mirror and concave mirror as an optical system, the optical system is large in the back-and-forth direction with respect to the line of sight. In addition, since the electrical circuit is arranged above the optical system, the dimension also becomes larger in the vertical direction to result in poor portability. This degrades the portability and makes it difficult to carry the apparatus in a pocket. Furthermore, since a half mirror is used, no bright screen display is possible.
In Japanese Laid-Open Patent Application No. 7-104209, an apparatus uses a sculptured surface prism to reduce the dimensions of the optical system and obtain light fitting properties. However, much improvement is required to carry the apparatus in a pocket or for portable use as an HMD.
In the portable image display apparatus disclosed in Japanese Laid-Open Patent Application No. 8-327920, since the optical system is formed by overlapping lenses in the direction of line of sight, and the electrical circuit board is arranged in the direction parallel to line of sight, the dimension in the back-and-forth direction becomes large.
It is an object of the present invention to provide an image display apparatus which solves the above-described problems and realizes small dimensions and excellent portability.
Other objects, features, and advantages of the present invention will become apparent from the following description of preferred embodiments in conjunction with the accompanying drawings.